1. Field of the Invention
This invention relates to an X-ray detector used in an X-ray Computerized Tomography (CT) scanner or the like for converting X-rays into light by means of a scintillator and converting light from the scintillator into an electric signal by means of a photoelectric converter.
2. Description of the Related Art
A multi-channel type X-ray detector is used in X-ray scanners of a second- or succeeding-generation model. An ion-chamber type detector is frequently used as a conventional multi-channel type detector. However, recently, an X-ray detector of solid-state detector type which can be made small and lightweight and whose detection efficiency may be enhanced is used. The solid-state detector has photodiodes of a multi-channel type disposed on a base plate and scintillators arranged thereon for respective channels. Collimators are disposed on the boundaries between the scintillators of respective channels irradiated in a direction perpendicular to the scintillators. When X-rays come into the scintillator of each channel, scintillation light corresponding to the incident X-rays is generated from scintillator and converted into an electric signal by the photodiode, and the electric signal is supplied to a data acquisition system via an electrically conductive line disposed on the base plate.
In the above solid-state detector, use of the scintillator causes problems. That is, a phenomenon in which the scintillator is colored occurs when the X-ray radiation amount increases with an increase in the service time of the detector. The phenomenon is called a radiation damage phenomenon. The coloring phenomenon degrades the scintillation light transmittance efficiency of the scintillator, thereby lowering the detection sensitivity. Further, the colored portion appears in the detection output as the past X-ray radiation history, and consequently, an artifact may appear in the reconstructed tomographic image. The above drawbacks are occurred in other types of X-ray detectors using the scintillator.